UV exposure has increased over the last 30 years, but stabilized since the mid-1990s
From NASA Goddard press release here
NASA scientists analyzing 30 years of satellite data have found that the amount of ultraviolet (UV) radiation reaching Earth’s surface has increased markedly over the last three decades. Most of the increase has occurred in the mid-and-high latitudes, and there’s been little or no increase in tropical regions.
The new analysis shows, for example, that at one line of latitude — 32.5 degrees — a line that runs through central Texas in the northern hemisphere and the country of Uruguay in the southern hemisphere, 305 nanometer UV levels have gone up by some 6 percent on average since 1979.
The primary culprit: decreasing levels of stratospheric ozone, a colorless gas that acts as Earth’s natural sunscreen by shielding the surface from damaging UV radiation.
The finding reinforces previous observations that show UV levels are stabilizing after countries began signing an international treaty that limited the emissions of ozone-depleting gases in 1987. The study also shows that increased cloudiness in the southern hemisphere over the 30-year period has impacted UV.
Jay Herman, a scientist at NASA’s Goddard Space Flight Center in Greenbelt, Md., stitched together data from several earth observing satellites — including NASA’s Aura satellite, NOAA weather satellites, and commercial satellites — to draw his conclusions. The results were published in the Journal of Geophysical Research in February.
“Overall, we’re still not where we’d like to be with ozone, but we’re on the right track,” said Jay Herman. “We do still see an increase in UV on a 30-year timescale, but it’s moderate, it could have been worse, and it appears to have leveled off.”
In the tropics, the increase has been minimal, but in the mid-latitudes it has been more obvious. During the summer, for example, UV has increased by more than 20 percent in Patagonia and the southern portions of South America. It has risen by nearly 10 percent in Buenos Aires, a city that’s about the same distance from the equator as Little Rock, Ark. At Washington, D.C.’s latitude — about 35 degrees north — UV has increased by about 9 percent since 1979.
The southern hemisphere tends to have more UV exposure because of the ozone hole, a seasonal depletion of the ozone layer centered on the South Pole. There are also fewer particles of air pollution — which help block UV — due to the comparatively small numbers of people who live in the southern hemisphere.
Despite the overall increases, there are clear signs that ultraviolet radiation levels are on the verge of falling. Herman’s analysis, which is in agreement with a World Meteorological Report published in recent years, shows that decreases in ozone and corresponding increases in UV irradiance leveled off in the mid-nineties.
The Many Sides of Radiation
Shorter ultraviolet wavelengths of light contain more energy than the infrared or visible portions of sunlight that reach Earth’s surface. Because of this, UV photons can break atmospheric chemical bonds and cause complex health effects.
Longer wavelengths (from 320 to 400 nanometers) — called UV-A — cause sunburn and cataracts. Yet, UV-A can also improve health by spurring the production of Vitamin D, a substance that’s critical for calcium absorption in bones and that helps stave off a variety of chronic diseases.
UV-B, which has slightly shorter wavelengths (from 320 to 290 nanometers), damages DNA by tangling and distorting its ladder-like structure, causing a range of health problems such as skin cancer and diseases affecting the immune system.
As part of his study, Herman developed a mathematical technique to quantify the biological impacts of UV exposure. He examined and calculated how changing levels of ozone and ultraviolet irradiance affect life. For Greenbelt, Md., for example, he calculated that a 7 percent increase in UV yielded a 4.4 percent increase in the damage to skin, a 4.8 percent increase in damage to DNA, a 5 percent increase in Vitamin D production, and less than a percent of increase in plant growth.
“If you go to the beach these days, you’re at slightly higher risk of getting skin cancer (without protection),” Herman said, though he noted the risk would have been even greater in the absence of regulations on ozone-depleting substances.
Last year, one of Herman’s Goddard colleagues, Paul Newman, published a study showing that the ozone hole likely would have become a year-round fixture and UV radiation would increase 650 percent by 2065 in mid-latitude cities if not for the Montreal Protocol, an international treaty signed in 1987 that limited the amount of ozone-depleting gases countries could emit.
Clouds and Hemispheric Dimming
In addition to analyzing ozone and ultraviolet trends, Herman also used satellite data to study whether changes in cloudiness have affected UV trends. To his surprise, he found that increased cloudiness in the southern hemisphere produced a dimming effect that increased the shielding from UV compared to previous years.
In the higher latitudes especially, he detected a slight reduction — typically of 2 to 4 percent — in the amount of UV passing through the atmosphere and reaching the surface due to clouds. “It’s not a large amount, but it’s intriguing,” Herman said. “We aren’t sure what’s behind it yet.”
Vitali Fioletov, a Canadian scientist and member of the World Meteorological Organization’s advisory group on ultraviolet radiation, agreed that Herman’s findings about cloudiness warrant additional investigation. “I found the cloud effects on the global scale to be the most interesting aspect of the study,” he said. “This isn’t something you could see without satellites.”
Herman synthesized measurements from the Total Ozone Mapping Spectrometer (TOMS) aboard Nimbus 7 and Earth Probe, the Ozone Monitoring Instrument (OMI) on NASA’s Aura satellite, NASA’s Sea-Viewing Wide Field-of-view sensor (SeaWiFS) on the commercial SeaStar satellite, and the Solar Backscatter Ultraviolet Instrument (SBUV) on several polar orbiting NOAA weather satellites.
Related Links:
Global increase in UV irradiance during the past 30 years (1979–2008) estimated from satellite data
h/t to Dr. Leif Svalgaard
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And I have to agree with Christian S. I have read a lot that challenges the assumption that the ozone layer used to be thicker, just like the assumption that it used to be cooler.
Mad dogs!
@davidmhoffer (09:07:11) :
O3 filters UV, but not all
O2 mostly lower in atmosphere than O3
UV strikes O2 breaking the molecules up and producing O3
O3 layer increases in size
filtering out more UV
resulting in less O3 production
[etcera]
– – – – – –
Excellent! I was aware of the Oxygen-Ozone cycle, but your explanation is the clearest I’ve ever seen. It’s interesting that at ground level, Ozone is considered pollution, but in the layer, it’s considered life saving. BTW, operation of fluorescents (including compact fluorescents) increase ground level Ozone pollution inside of buildings.
R.Gates
“Yes, there are a very few who are trying to capitalize on the AGW hypothesis (or hype, if you prefer), but for every one of those, there are 100 or even 1,000 honest researchers who meticulously gather data, record it, have their findings peer reviewed, and then publish. This is probably what turns me off the most about AGW skeptics…too much distrust, when only a little skepticism and “prove it to me” attitude is required and even necessary to keep the science honest throughout. Hence I am 75% convinced the AGWT is correct, and a 25% skeptic. This 25% drives my climate research friends crazy, as I am always asking questions, but in addition to making them ticked off at my stupid questions, I at least hope it makes them take an occasional brief moment to consider other interpretations of their data though they never waiver from being 95 to 99% certain that AGWT is correct. But I do sense that many skeptics are 100% certain that AGWT is incorrect, and this kind of certainty scares me even more…
I think you are extrapolating a little far from your few acquaintences on both sides of the divide.
I am a sceptic but also a physicist: so I am not 100% sure of anything!
Moreover I have yet to meet a so called climate researcher who is a sufficiently expert physicist to be even 50% sure of what is an extraordinarily complex system. Your friends may be right in their beliefs but this would be just luck: their 95+% certainty is a delusion.
The problem for me is that physics is based on postulating theories which can be tested by experimentation. The climate does not allow this. So we have to rely on natural variation to give us clues to the mechanisms that control it. Correlation does not prove causality so for this type of evidence to be convincing it has to be uneqivocal.
There is no doubt that CO2 absorbs 14-18 micron radiation but, so far, I have not seen a single piece of evidence which links this effect to temperature changes in the real world. Indeed, as it has been pointed out by a host of experts on this blog already, many of the “signature” predictions, such as a warming mid troposphere, have not materialised.
On the other hand the evidence from the ice core records clearly show that rises in temperature have previously always occured when CO2 has been relatively LOW. I believe this is just coincidence since these rapid temperature rises have been after ice ages when the CO2 is always low. But it suggests to me that there are drivers of climate far more powerful than this one even if it does exist. Until someone comes up with an explanation for the huge shifts in climate over the millenia that clearly do not involve CO2 I will find it hard to be convinced that these forces are not still active now and playing a role in what are, on any historic basis, tiny flucuations in temperature.
>> R. Gates (21:54:34) :
Robert Austin said:
“CFC scare looks too much like a practice run for the main event, climate change…”
Sorry, this is too grassy knoll for me. Since I personally know several scientists in the climate research field and know how dedicated they are, and have been since their undergraduate days, I simply don’t accept a conspiracy notion. <<
The 'conspiracy' is not by the scientists, but by the politicians seeking more control over our daily lives. They demand results that will give them a reason to grab power, and are willing to pay well (out of other people's pockets) to get what they want.
The climate scientists are the beneficiaries of this to the tune of over $2B per year. They are more like religious leaders than true scientists, because they start with AGW as a basic truth. I wouldn't claim that a priest is not dedicated, nor that he was knowingly promulgating false information. Nonetheless, it's not science when the goal is to gather evidence to support a belief and no research is done in the direction of disproof.
The word ‘conspiracy’ implies too much in regards to climate change science. It implies complicity, or ‘that all of those involved are in on the scheme’, which is hardly the case. Most scientists are simply doing what comes naturally and bristle at the accusation of a conspiracy as much as climate realists bristle at the word ‘denier’.
Research scientists need funding to do their work. Right now, almost all of that comes from government. Government, in turn, is run by politicians who need votes to keep their jobs. They get votes by convincing the voting public that they are doing something to solve problems. Consequently, if something is perceived to be a problem, research on that topic is funded. If it is not a problem, (or has no foreseeable benefit) it does not get funded very much, if at all.
Scientists have no qualms adding words to their studies that relate their work to a ‘fundable’ topic, even if there is no correlation. For example, this site has posted a report on a study of Sequoia tree rings in which the authors state:
“Knowing how giant sequoia trees responded to a 500-year warm spell in the past is important because scientists predict that climate change will probably subject the trees to such a warm, dry environment again…”
The study indicates that the theory of AGW may be wrong, but the authors avoid making such statements. Instead, they tie there study to the ‘problem’ of AGW. There is no scientific reason for the above quote, only a financial one. The speculative quote is not ‘wrong’ per se, only scientifically unwarranted. Such quotes exist in almost every climate study, allowing Oreskes to conclude that the vast majority of the science supports the AGW theory, even if the science is actually disproving the theory.
What the vast majority of research scientists support is additional funding and further employment. It is simply the way the system has been set up. It is a bad system if your goal is good science, but it is not a conspiracy.
Enneagram (11:56:07) : Thanks.
This sounds a very sciencey experiment!
@Henry chance (08:15:54) :
“WASHINGTON — It may sound far-fetched, but federal regulators are studying whether sudden acceleration in Toyotas is linked to “cosmic rays”.”
– – – – – – –
A bit OT – Cosmic instead of UV – but I’ll add that the cosmic particle scenario is plausible, but usually only for volatile DRAM (Dynamic Random Access Memory). DRAM is susceptible since each data bit is held by the charge stored in a tiny capacitor rather than in a transistor gate, and the capacitor’s state is constantly refreshed, usually at intervals in milliseconds. If a cosmic particle (which still has a high enough energy level to ionize a molecule) strikes a DRAM capacitor with a state = 1 (charged), it will ionize the dielectric, causing it to become conductive. This discharges the capacitor, possibly changing the state of the bit. It will change the bit and produce a response if the capacitor remains discharged for a long enough interval before it is refreshed. If the state = 0 (discharged) when struck, no effect. Mysterious computer freezes requiring a reboot is sometimes due to a cosmic particle strike. The cosmic particle almost never does any lasting damage, thus after the event has passed and the circuitry has been powered down then rebooted, no amount of testing can ever confirm what occurred. To be virtually immune to cosmic particles, you would need to shield the circuitry with several inches of lead (Hardly ever done on the ground except for mega-expensive installations. Even $100k lab instruments don’t bother with lead shielding). Another way of dealing with it is to build redundancy into critical circuits. That’s one reason why the Space Shuttle originally used three computers, and now uses four. Cosmic particle strikes are more likely to occur at a higher elevation than at sea level, since it’s the atmosphere that does most of the attenuation. One estimate that I’m familiar with is that a desktop computer at sea level will suffer one cosmic particle strike that causes a malfunction during an 8 month period.
One of the main reasons the sun is stonger in the southern hemisphere over the summer than it is for the northern is the eccentricity of the earth’s orbit. From memory it is about 2% closer in January than June. Back in the 60s, when I lived in Canterbury, the skies were often red from the bushfires in Australia so there must have been significant pollution. I don’t know if that affected the sunburn rate.
“Fly to New Zealand and do a couple of hours work in my garden with your shirt off without sunblock. After we get you back out of the hospital you won’t want to talk about “there’s no ozone hole”.”
I moved to New Zealand 21 years ago, and I must say that my personal experience is that burn times are not as bad now as they were in the 1989-2000 period. In that period burn times were in the 15-30 minute range.
I regularly mountain bike for 3-4 hour stretches, without either sunblock or sunburn (something I would never have attempted a few years ago).
In the early 90’s Hawkes Bay used to get 2-4 days per summer when temperatures would hit 40 degrees C. I have not seen anything in excess of about 33 for several years now, even though there have been a number of very good weather summers.
The current summer has not been a great one in the center of the North Island (though the far north is having a drought). In Rotorua the weather in February was wetter and cloudier than normal. However, the radio reported that the month was warmer than average, because the minimum temperatures were not as low as average. Of course, the cloud that stopped the nights cooling also prevented the days getting anywhere near as hot as normal!
Had the measurement been based upon noon time temperatures I am sure the month would have been classed as below average.
It got me wondering how “average” temperatures are measured in desert regions, since the clear skies mean that in a 24 hour period the temperature will go from scorching hot to almost freezing. Is it by day time temps or night time or by a combination of the two?
I was reading a few months ago about the theory that low sunspot counts allowing cosmic radiation that causes high altitude cloud formation. If this is the case, would that cause a reduction in UV radiation reaching the surface?
JER0ME (02:38:06) :
“Biggest two causes of skin cancer in my belief:
1. People who do not spend time in the sun maxing out on two weeks in the sun.”
I agree completely.
In New Zealand there is a big push each year to get people (especially children) to “slip slop slap, cover up and stay out of the sun in the hot part of the day.”
I actually think this is making the problem worse, because people live sedentary lives, mainly indoors, and they never condition their skin to the sun, so they never allow their body to build up the natural defenses to UV.
Because of this they are totally unprepared for those times when they do get caught out in the sun for a period without any protection (and it invariably happens).
The people I see with sunburn are usually the ones who are habitually the most cautious, who have just got unlucky that one day (I have been in that position myself)…..
I am not against sunscreen and taking sensible precautions. I just think that much of what is attributed to stronger UV levels is actually little more than the consequence of lifestyle changes.
As an Irish redhead, I don’t tan very well. Can you protect yourself by exposing your skin to UV’s? I certainly did growing up. And then grownup life caused me to work instead of play. I was in the Sun 24/7 growing up, in high altitude, and without any kind of skin protection. Then I stayed out of the sun because there was no more play time for me. At the age of 49, I nearly lost my lip to cancer. Was it the UV exposure early on? Was it not the Sun later on? Don’t know. Anecdotal evidence belongs in jokes as the punch line, but is NOT deserving of scientific conclusions.
The conspiracy theory is a bit too far in my opinion. For the most part, I believe that AGW scientists believe they are on to something, but have made the mistake of narrowing their field of vision to focus just on proving themselves right. Thus opposite opinions are not considered or used to inform their research.
I have experienced this. I am in an unpleasant discussion with a school psych. Our opinions differ. This person holds to an immovable opinion because the person’s background is in psychometric measurement. I hold to mine because my background is cross-disciplinary. Each opinion is worth considering and I value the opposite opinion. But because my approach to evaluating a student is cross-disciplinary, I see a mismatch between IQ scores, and several of the other measurements, as well as in my observations. Therefore I need more information, which I believe is the proper way to approach what the “data” says. If there is any area of investigation that absolutely requires a skeptic’s eye to “data”, it has to be in the process of assigning disability labels to children.
Dead on, IMO.
Quoting from http://www.nas.nasa.gov/About/Education/Ozone/radiation.html
“Ultraviolet levels are over 1,000 times higher at the equator than at the polar regions”
For the sake of the following points lets assume an even declination in UV exposure the further north/south of the equator you go. Equator = 1000, poles = 1.
So if you divide the lines of latitude (90) into 1000 then you get 11.11… times (1011% increase/decrease per degree N/S) the UV for every degree closer you move to the equator. Now a degree of latitude is 69 miles (111km). The distance from New York to Boston is about 200 miles (~2.89 degrees), so the UV difference between NY and Boston is roughly (2.89 X 11.111 =) 32.21 times…
So moving south to Boston from NY is a FAR greater UV risk (3121% increase) than the 6-35% increase these characters are trying to alarm us over.
I saw opinions above about how easily one does (or does not) char in Australia.
Syndey AU is at 30 degrees latitude S, Paris (France) is at 48 degrees latitude N and Rome (Italy) is 41 degrees N – do the math (11 degrees difference to the equator = 122 times UV or a 12100% increase), it is a small wonder that people burn more easily in AU, they are CLOSER to the equator than the people in Europe!
Fear mongering indeed.
Bah! Humbug!
Something about this article has been bothering me since it appeared. I finally figured out what it is.
Where is the trend line?
If someone tried to post the temperature in 1979 and in 2009 and draw conclusions about an “increase” this blog would be up in arms. What about the data points in between?
Has there been a steady increase? Or exponential?
Was there a peak at some point? If so how long ago?
Does the trend line mirror the sun spot record? the temperature record? ozone level records?
Since the data clearly exists by latitude, I would think that trending it by latitude would be easily accomplished. Looking at it in isolation however makes little sense. The UV emissions from the sun vary with sun spot activity. So the change since 1979 in regard to ozone is meaningless unless fluctuations in comparison to sun spots are also understood.
(and if there is a big peak or trough in the record there might be some ‘splaining to do)